Voltage regulator



April 6, 1943. J. M. WEED VOLTAGE REGULATOR Filed Oct. 23, 1940 oooo oobo Inventor James ,M. Weed, 10 W 6. J

s Attorney.

Patented Apr. 6, 1943 OFFICE VOLTAGE REGULATOR James M. Weed, Schenectady, N. Y.. asslgnor to General Electric Company, a corporation of New York Application October 23, 1940, Serial No. 362,398

6 Claims.

This invention relates to voltageregulators and more particularly to improvements in transformer type voltage regulators for alternating-current circuits.

Electricity is today distributed commercially almost entirely by alternating current at a constant frequency and constant voltage. The usual frequency is about sixty cycles per second and the usual utilization voltage is about 110 volts. The frequency is maintained constant by means of accurate and sensitive speed regulating means for the prime movers of the alternating-current generators and so long as the speed of the generators is maintained constant the frequency at the load will not vary no matter how the load varies or how long the line is between the load and the generator. The voltage is maintained constant by voltage regulators for the generators and also by voltage regulators inserted in the. transmission and distribution circuits between the generators and the load. These latter regulators can correct for the voltage drop in the impedance of the transmission and distribution circuits and they can maintain constant voltage at variable load at any predetermined point on a distribution system. However, it is obviously impractical to connect all of the loads to any particular point on a distribution system so that it is usually necessary to set such regulators to hold voltage at a certain point known as the load center to which a number of loads are connected through individual circuits of diiierent impedances. The voltage drops in the impedances of these circuits result in objectionable variations in load voltage.

In accordance with my invention I provide a novel, simple and inexpensive automatic voltage regulator which is particularly adapted for connection in a secondary circuit of an alternatingcurrent distribution system directly at or very close to the point of connection of an individual or particular load thereto. An example of such a load would be a private residence.

An object of the invention is to provide a new and improved transformer type automatic voltage regulator.

Another object of the invention is to provide an automatic voltage regulator for secondary distribution circuits which will be low in cost and reliable in operation.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 illustrates a particular embodiment of my invention, Fig. 2 is a detail by means of the switches 4-1, inclusive.

view of a toggle switch mechanism suitable for use in. Fig. 1, Fig. 3 is a circuit diagram of a modification for reducing the voltage difference between the neutral of the secondary winding of a three-wire distribution transformer and the neutral of the regulating transformer, and Figs. 4 and 5 are circuit diagrams of further modifications for eliminating this voltage difference.

Referring now to the drawing and more particularly to Fig. 1, there is shown therein a regulating autotransformer I connected to a threewire single-phase load circuit 2. The transformer is provided with a plurality of taps3 connected each to one of the fixed contacts of a series of single pole double throw switches 4, 5, 6 and I respectively. A second fixed contact of each of the switches 4, 5 and 6 connects to the movable contact of the switch of next higher nu-' merical order, while the second fixed contact of switch I connects to tap 3'. A supply circuit 8 has one side thereof connected to one terminal of the transformer l and the other side is selectively connectable to different ones of the taps 3 These switches are toggle-actuated spring snap switches, each of which is provided with an operating lever or handle 9. These handles are engaged by a slot II in a rotatable member N, which slot is constructed with a gradual offset in the radial direction at its mid portion. By reason of this offset, rotation of the disk in one direction will cause successive operation of the switches 4, 5, 6 and 1 anda reverse rotation will cause their reversed successive operation. Of course, if the disk is stopped at any intermediate point, no further operation of the switches will take place until the disk is moved again. These switches may be standard switches of this type, such as are used in numerous control circuits or relays. The details of a simple form suitable for use in my invention are shown in Fig. 2. In regulators of small size or for high power factor loads it is unnecessary to provide any bridging means to prevent arcing and, by reason of the rapid action of these switches, taps on the transformer I can be changed by breaking one contact before making another without producing any noticeable lamp flicker.

In 1 the switches are so positioned that the entire autotransformer is connected across the supply circuit 8. Operation of the switch 4 by the rotation of the disk In in a counterclockwise direction will remove a certain number of turns from this circuit, thus increasing the load circuit voltage. Additional increases in this voltage are eiIected by successive operation of switches I, 8 and 1 in the same manner. Similarly, as these switches are restored to their illustrated positions by a reverse rotation of disk III the load circuit voltage will be lowered in increments predetermined by the tap spacing.

The disk "I may be driven directly by a reversible motor such, for example, as a motor made up of two motor elements of the type described and claimed in Warren Patent 1,495,827. One of these motor elements is shown at I2 and the other at l3.

The motor elements l2 and I3 may be automatically controlled in response to the load circuit voltage by means of a voltage sensitive relay l4 having an operating magnet l5 connected across the load circuit. This magnet attracts a spring restrained armature I6 carrying a contact which normally floats between a pair of fixed contacts connected respectively to terminals of said motor elements. The remaining motor terminals are connected together to one side oi the load circuit and the floating contact is connected to the neutral of the load circuit. The relay is so adjusted that when the load circuit voltage is normal the floating contact is not in engagement with either of the flxed contacts so that both of the motors are de-energized. If now the load voltage rises or falls, the armature moves toward or away from the magnet l5 until it engages one or the other of the fixed contacts, thereby energizing the motor element which causes the disk Hi to turn in the direction which will restore the load voltage to normal by the operation of the necessary switches. When the load voltage returns to normal the voltage relay interrupts the motor circuit and the regulator comes to rest.

Most secondary distribution circuits are threewire circuits so that if the supply circuit 8 is connected to the secondary winding of a conventional distribution transformer, this winding will be provided with a neutral point which ordinarily will be grounded. Therefore, if the neutral conductor of the load circuit 2 should be grounded, an objectionable current will flow bedisk I0 is rotated in the direction to cause successive operation of the switches, switch 4 will operate first. This will produce some voltage diflerence between the neutrals but further rotation of the disk will cause operation oi switch 5, which will restore the-symmetry oi the connections on the primary side of the regulator and cancel the said voltage difference. This cycle will be repeated by the operation of switches and I. -It will be seen that by thus arranging the switches in two groups for changing taps at the two ends of the winding, and by operating 3 the switches in the two groups alternately, the

potential difference between the neutrals will never exceed a relatively small value of the order of a fraction of the tap-to-tap voltage.

In some cases even this relatively small voltage difference between the neutrals may produce an objectionably high current. In that case the neutral current may be further reduced'by shliting the neutral by an amount corresponding to a fraction of the tap voltage such, for example, as one-fourth of the tap voltage. This will be done in Fig. 3 by shifting a switch l8 to its downward position. The resulting asymmetry, before the operation of any switches, will result in a voltage difference between the neutrals of. onetween the two neutrals, through ground, by

reason of a voltage difference between the two neutrals resulting from the operation of the tap-changing switches. With the switches in the position illustrated in the drawing this voltage difference is zero but, if any one or more of the switches is operated, it will be apparent from the drawing that the connections on the primary and secondary sides of the autotransformer I will be unsymmetrical, resulting in a voltage difference between the neutral points of the input and output circuits. Furthermore, the magnitude of the difference in voltage'between the two'neutrals will progressively increase as more of the switche are successively operated.

One way of minimizing this difficulty is shown in Fig. 3. In this figure the supply circuit 8 is connected to the outside wires of the three-wire secondary of a conventional distribution transformer II. The regulator has been modified by having two sets of taps, one at each end of the autotransformer winding, and by having switches 4 and 6 connected to one set of taps and switches 5 and I connected to the other set of taps. The neutrals of both the distribution transformer l1 and the regulator l are grounded. With the switches in their illustrated positions there will be no difference in the neutral voltages and no objectionable current. It now the half of that existing after the operation of switch 4 with the neutral switch I! in the upward position. If now switch 4 is operated, the same voltage difierence will exist, but with reversed polarity. Subsequent operation of switches 5, 6 and I successively will, in each case, reverse the polarity of this voltage diflerence without changing its value. Thus, the maximum voltage difference between neutrals which exists with the neutral switch l8 in the upward position in Fig. 3 may be halved with the switch in its downward position, but this reduced voltage difierence will always be present with one polarity or the other.

Ii no difference between the neutral voltages can be tolerated, this result may be obtained with the arrangement shown in Fig. 4, in which taps are provided at both ends of the winding as in Fig. 3, but duplicate switches 4 and 5' have been added and these switches are arranged to operate simultaneously with the corresponding switches 4 and 5. This might easily be done by mounting the switches 4' and 5' on the opposite side of the disk from switches 4 and 5 so that the operating levers of switches 4 and 4' are opposite each other in the slot II and the operating levers of the switches 5 and 5 are opposite each other in the slot II. In this manner, switches 4 and 4 operate simultaneously and subsequently switches 5 and 5' will operate simultaneously, with the result that the voltages of the two neutrals stay the same.

In Fig. 5 there is shown another modification for accomplishing the same result as in Fig. 4. This is done by means of double-pole doublethrow switches 4" and 5" which are so connected that they change taps simultaneously and symmetrically on opposite sides of the neutral or midpoint of the autotransiormer winding. These switches 4" and 5" are Operable by the same snap action toggle mechanism as are the single pole switches already described. The connections of one set of poles of these switches are the same as those of switches 4 and I in Fig. 4 and the connections of the remaining set of poles of the switches 4" and 5" are the same as the connections of the switches 4' and I.

Of course, as many switches and re ular taps may be added in Fig. as may be necessary to maintain the load circuit voltage constant. This may be said, also, with respect to Fig. 4 and, it necessary, with respect to Figs. 1, 2 and 3.

While there have been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an altemating-current supply circuit having a grounded neutral and havin a pair of outer conductors, a voltage regulating autotransformer having a grounded neutral, said autotransi'ormer also having two sets of equally spaced taps located respectively on opposite sides of its grounded neutral, switching means for selectively connecting said conductors to different taps in said sets respectively, and means for controlling said switching means so as to prevent variations in the magnitude of the voltage differ ence between said neutrals. 1

2. In combination, a single-phase three-wire secondary distribution circuit having a grounded neutral, a voltage regulating autotransformer, said autotransformer having its terminals connected to a load circuit all of whose current is supplied by said autotransformer and having an intermediate point grounded, means for connecting one side of said distribution circuit to said autotransformer on one side of said intermediate point, means for connecting the other side of said distribution circuit to said autotransformer on the opposite side of said intermediate point, and means for alternately changing the points of connection of said sides of said distribution circuit to said autotransformer, said points being uniformly located asymmetrically with respect to said intermediate point so that the voltage difference between the neutral of said distribution circuit and said intermediate point is of the same magnitude for all of the particular sets of said points on opposite sides of said intermediate point which are in circuit at any time.

3. In combination, a single-phase three-wire distribution circuit having a grounded neutral, a voltage regulating autotransformer having a grounded neutral point and having separate sets of equally spaced taps on both sides of said neutral point, switching means for connecting the conductors of said distribution circuit respectively to taps on opposite sides of the neutral point of said transformer, the neutral point of said transformer being so located that its voltage differs from the voltage of a point electrically midway between said last-mentioned taps by onefourth the tap-to-tap voltage, and means for operating said switching means so asalternately to change the connections of said conductors from tap-to-tap in their respective. sets of taps. 4. In combination, a distribution transformer having a single-phase three-wire grounded neutral secondary circuit, a regulating autotransformer having its electrical midpoint grounded, means for selectively connecting one side of said secondary circuit to spaced taps on said autotransformer on one side of said electrical midpoint, and means for simultaneously connecting the other side of said secondary circuit to correspondingly located taps on said autotransformer on the opposite side of its electrical midpoint.

5. In combination, a transformer having a winding provided with a plurality of taps, at

least two single pole double throw snap switches each having a pair of fixed contacts and a movable contact, common operating means for actuating said switches successively, and a circuit for said winding having one conductor connected to the movable contact of one of said switches, one of the fixed contacts of said last-mentioned switch being connected to one of said taps and the other fixed contact of said switch being connected to the movable contact of another of said switches, the fixed contacts of said other switch being connected respectively to diiierent ones of said taps.

6. In combination, an electric circuit, a transformer connected therein and provided with a neutral point and with two sets of equally spaced taps, said sets being located respectively on opposite sides of said neutral point, and switching means for alternately electrically removing from or inserting in said circuit sections of said winding between adjacent taps in said sets of taps, said neutral point being displaced one-fourth the tap to tap voltage difference from the electrical midpoint of said winding whereby operation of said switching means alternately reverses the polarity of the said voltage diiierence without changing its magnitude.

JAMES M. WEED. 

